rpcclient: fix race in TestWSClientNonBlockingEvents

The race is probably caused by the fact that accessing receivers
list of WSClient under rlock requires some time. Technically, it may
be helpful to increase timeouts for the receivers checking operation,
but we can add one more condition to ensure that at least maximum
number of messages was received by the buffered receiver.

This test can't be reproduced on my machine, thus I'd suggest to keep
an eye on it in GH workflows for some time.

Close #3005.

Signed-off-by: Anna Shaleva <[email protected]>

pkg/rpcclient/wsclient_test.go

@@ -345,7 +345,13 @@ func TestWSClientNonBlockingEvents(t *testing.T) {
 		return blocksSent.Load()
 	}, time.Second, 100*time.Millisecond)
 
-	// Check that block receiver channel was removed from the receivers list due to overflow.
+	// Check that block receiver channel is full.
+	require.Eventually(t, func() bool {
+		return len(bCh) == chCap
+	}, 2*time.Second, 200*time.Millisecond)
+
+	// Check that block receiver channel was removed from the receivers list due
+	// to overflow.
 	require.Eventually(t, func() bool {
 		wsc.subscriptionsLock.RLock()
 		defer wsc.subscriptionsLock.RUnlock()